1. Field of the Invention
The present invention relates generally to a method and apparatus for producing a three-dimensional object in which an exposure beam is irradiated on a liquid photo-curable resin to produce a three-dimensional object on the basis of a desired three-dimensional object image. More particularly, this invention relates to a method and apparatus for producing a three-dimensional object in which a liquid surface of a liquid photo-curable resin is exposed in response to the shapes of planes exploded from a certain direction of a three-dimensional object image to thereby form a cured resin layer and in which the cured resin layer is sequentially laminated, thereby a three-dimensional object being formed. Furthermore, the present invention relates to a method and apparatus for producing a three-dimensional object in which a scanning of beam on the liquid surface of a liquid photo-curable resin is performed by switching between two kinds of scanning systems to thereby produce a three-dimensional object whose surface is smooth, and in which a three-dimensional object can be produced at high speed.
2. Description of the Prior Art
In the prior art, it is proposed to produce a product of a desired shape by irradiating a liquid photo-curable resin with a predetermined exposure beam. For example, U.S. Pat. No. 4,041,476 and Japanese Patent Application No. 63-267945 describe such a previously-proposed method.
FIG. 1 shows an example of a three-dimensional object producing apparatus a which embodies the above-described method.
It will be seen in FIG. 1 that a resin storage tank b is provided to store therein a liquid photo-curable resin c which is cured by the radiation of a predetermined exposure beam, for example, ultra-violet (UV) rays. An elevator d is provided with a horizontal, plate-shaped stage e, and this elevator d is moved up and down by some suitable moving means (not shown). A beam scanner f is located above the resin storage tank b and allows an exposure beam g to be converged on a liquid surface h of the liquid photo-curable resin c. A shape-forming controller i is provided, and the scanning of the exposure beam g is performed on the liquid surface h by the beam scanner f under the control of the controller i and the movement of the elevator d is also performed under the control of the controller i.
When forming a predetermined three-dimensional object, at first, the elevator d is moved to the initial position, as shown by a solid line in FIG. 1, such that the liquid photo-curable resin c of a predetermined thickness (this thickness will be described more fully later) is located on the stage e of the elevator d.
The scanning of the exposure beam g on the liquid surface h is performed next. In this scanning-process, a so-called raster scanning is performed with patterns corresponding to planes in which a desired three-dimensional object image j is exploded into a number of planes in a certain direction thereof. In the following description, the respective planes will be referred to as exploded planes.
When the scanning of beam g is carried out, the liquid photo-curable resin c is cured at a portion thereof irradiated with the beam g to produce one sheet-shaped cured-resin layer having a configuration corresponding to that of the exploded plane of the liquid surface h. The elevator d is moved downwards at a pitch corresponding to the exploded pitch in which the three-dimensional object image j is exploded into a number of exploded planes in a certain direction each time one sheet-shaped cured-resin layer is formed completely. The thickness of the liquid photo-curable resin c on the stage e in the initial state is selected to be equal to the above-described pitch. Accordingly, the liquid photo-curable resin of the thickness corresponding to one pitch amount flows to the upper surface of the cured-resin layer, and the scanning of beam is performed on the next exploded plane to thereby form other cured-resin layer. At that time, the above-described cured-resin layer is bonded to the former cured-resin layer. In this manner, a new cured-resin layer k is sequentially laminated on the cured-resin layer formed, and a desired three-dimensional object is formed by a number of laminated cured-resin layers.
According to the method for producing a three-dimensional object as described above, the three-dimensional object can be produced on the basis of the desired three-dimensional object image so that, as compared with a prior-art method for producing a three-dimensional object by utilizing a metal mold, a three-dimensional object can be readily produced as an experiment. Therefore, the development from the design stage to the mass-production stage can be readily carried out at low cost.
In the above-mentioned three dimensional object producing method, if the scanning of the exposure beam is performed according to the raster-scanning system, there arises the problem that the surface of the three-dimensional object formed is given irregularities.
FIG. 2 is a plan view conceptually illustrating one portion of the locus in which a scanning of the exposure beam is performed on a certain exploded plane. In FIG. 2, reference letters k, k, . . . designate main scanning lines of the exposure beam g, i.e., lines along which beam spots l, l, . . . are moved and reference letter m represents the configuration line of the corresponding exploded plane.
As is clear from FIG. 2, of the outer configuration of the cured-resin layer formed, on the portion extended in the direction perpendicular to the main scanning direction of the beam there appears one portion of each of the shapes of the end beam spots l, l, . . . of the beam main scanning lines k, k, . . . , which presents the irregular (i.e., concaved and convexed) configuration line on the above portion. Consequently, the surface of the three-dimensional object image formed by the collection of irregular configuration lines are caused to take very small concavities and convexities.
In addition to the above-described raster-scanning system, a so-called vector scanning system is known as one of the beam scanning systems. In this vector scanning system, a straight line-shaped main scanning direction is not provided uniquely but the scanning is performed while the scanning direction is being changed to the direction corresponding to vector data. This vector scanning system is frequently utilized, for example, by a picture drawing system which employs a polygon mirror and a movable picture drawing table or a picture drawing system which employs a so-called X-Y photo plotter.
Accordingly, if the scanning of the exposure beam 8 in this kind of the three-dimensional object producing method is performed according to the vector scanning system, then the configuration of the exploded plane can be drawn by lines formed of continuous beam spots moving in accordance with the extended direction of the configuration lines, i.e., lines having a directivity in the two-dimension. Therefore, it is possible to obtain a three-dimensional object whose surface is smooth.
However, in this method of producing a three-dimensional object, if the scanning of the exposure beam is carried out according to the vector scanning system, the vector-scan has the directivity in the two-dimensions so that, so long as the configuration line of the exploded plane is not a straight line, the directions of the beam spots must successively be changed to many directions, which needs plenty of time for scanning the plane of the same area as compared with the above-described raster scanning system.